Abstract 4139187: Electrophysiological and Mechanical Characterization of Human Ventricular Myocardium from Patients with Primary or Secondary Cardiac Hypertrophy

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Left-ventricular hypertrophy (LVH) is an adaptive condition to hemodynamic stress often involving the left ventricle (LV). This pathological condition is associated with clinical complications such as ventricular arrhythmias and diastolic dysfunction, the molecular and cellular mechanisms of which have been poorly investigated in the human heart. We collected myocardial samples from the upper interventricular septum of 132 patients with hypertrophic cardiomyopathy (HCM), 42 patients with aortic stenosis and severe LVH (AoS-LVH) and 12 non-failing non-hypertrophic patients with valve disease (NF-NH), who underwent myectomy operations at our cardiac surgery center. Samples were used to isolate single viable cardiomyocytes from the left ventricle to perform patch-clamp electrophysiological studies and intracellular calcium measurements with fluorescent dyes. Intact trabeculae were also dissected to perform isometric force measurements of electrically-stimulated twitches. Single-cell patch-clamp studies revealed a marked prolongation of action potential duration (APD) in HCM (N=82, mean APD at 90% repolarization=763±252ms at 0.5Hz) and AoS-LVH (N=22, APD90%=579±147ms) samples with respect to NF-NH (N=12, APD90%=447±88ms). In both HCM and AoS-LVH cardiomyocytes, APD prolongation was associated with increased late-Na + current with respect to NF-NH, while L-type Ca 2+ current was enlarged only in HCM samples. Ca 2+ -fluorescence studies revealed markedly slower Ca-transient (CaT) kinetics in myocardial samples from HCM (N=38, mean CaT 50% decay time at 0.5 Hz = 658±179ms) and AoS-LVH patients (N=9, CaT50%= 568±187ms), when compared with NF-NH samples (N=8, CaT50%=283±59ms), paralleled by elevated diastolic [Ca 2+ ]. Twitch force measurements in intact trabeculae revealed prolonged isometric contractions in HCM (N=78, overall twitch duration at 0.5Hz= 730±147ms) and in AoS-LVH patient-samples (N=24, TwD=669±116ms), as compared with NF-NH (N=7, TwD=511±73ms). Force-frequency relationship was flat in pathological samples, while NF-NH trabeculae showed a clear increase in twitch amplitude while increasing pacing rate to 2Hz. Our results suggest that the main features of functional cardiomyocyte remodeling (that is, changes in the expression and/or function of ion-channel and EC-coupling proteins) are qualitatively similar in primary vs. secondary LVH, albeit abnormalities are quantitatively more extensive in HCM samples.

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